1. Technical Field
Embodiments described herein relate to system in packages (SiPs) and methods for making SiPs. More particularly, embodiments described herein relate to systems and methods for shielding SiPs from electromagnetic interference.
2. Description of Related Art
An SiP (system in package or system-in-a-package) includes one or more integrated circuits enclosed in a single module (e.g., a single package). The SiP may perform many (or all) of the functions of an electronic system. SiPs are typically used inside smaller electronic devices such as, but not limited to, mobile phones, digital music players, and tablets. An example of an SiP may include several chips (e.g., a specialized processor, DRAM, and/or flash memory) combined with passive components (e.g., resistors and capacitors) mounted on a single substrate. Mounting all the components on the single substrate provides a complete functional unit that can be built in a multi-chip package and few external components may be needed to make the device work. A drawback to SiPs is that any defective chip in the package will result in a non-functional packaged integrated circuit, even if all the remaining modules in the same package are functional.
EMI (“electromagnetic interference”) is the unwanted effects in the electrical system due to electromagnetic (e.g., radio frequency (RF)) radiation and electromagnetic conduction. Electromagnetic radiation and electromagnetic conduction are different in the way an EM field propagates. Conducted EMI is caused by the physical contact of the conductors as opposed to radiated EMI which is caused by induction. Electromagnetic disturbances in the EM field of a conductor will no longer be confined to the surface of the conductor and may radiate away from it. Mutual inductance between two radiated electromagnetic fields may result in EMI.
Due to EMI, the electromagnetic field around the conductor is no longer evenly distributed (e.g., resulting in skin effects, proximity effects, hysteresis losses, transients, voltage drops, electromagnetic disturbances, EMP/HEMP, eddy current losses, harmonic distortion, and reduction in the permeability of the material).
EMI can be conductive and/or radiative and its behavior is dependent on the frequency of operation and cannot be controlled at higher frequencies. For lower frequencies, EMI is caused by conduction (e.g., resulting in skin effects) and, for higher frequencies, by radiation (e.g., resulting in proximity effects).
A high frequency electromagnetic signal makes every conductor an antenna, in the sense that they can generate and absorb electromagnetic fields. In the case of a printed circuit board (“PCB”), consisting of capacitors and semiconductor devices soldered to the board, the capacitors and soldering function like antennas, generating and absorbing electromagnetic fields. The chips on these boards are so close to each other that the chances of conducted and radiated EMI are significant. Boards are designed in such a way that the case of the board is connected to the ground and the radiated EMI is typically diverted to ground. Technological advancements have drastically reduced the size of chipboards and electronics and locating SiPs along with other components closer and closer together. The decreasing distances between components, however, means that chips (e.g., SiPs) are also becoming more sensitive to EMI. Typically electromagnetic shielding is used to inhibit EMI effects. However, EMI shielding for SiPs may be difficult and process intensive to integrate into the SiP structure.
Many current shielding implementations use a post-singulation metal deposition process (e.g., sputtering or plating) to form the EMI shield on an SiP structure. Post-singulation metal deposition, however, relies on the metal deposition process connecting the deposited metal with ground layers in the substrate of the SiP. Making such connections may be difficult for thin substrates and may require special handling and sputtering equipment.